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I put a white sheet round it to reduce photosynthesis, but doesn't cover the top and is probably to thin to completely stop it. Anyway it's the first time for 2 years and was ready. Red mildew in it! Hasn't affected the cleaning results, but it was a tad yucky to say the least! Hopefully I'll have it covered with wood for frost protection soon, time will tell if it will still go manky!

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In North Wales we have a red peaty coloured rain but the growth in the tank with uv light is green.
How much gung was in it, aint cleaned mine for 5 years now :blink:

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It just about covered the base of the tank, on the sides got thinner as it went up, to about the 300 mark. There was a bit of green too, the red stood out though! As I said, didn't affect the water quality, just clung to the plastic, nothing "in" the water as such. Can't for the life of me figure out why it's red.